Rails 5.2 Active Storage add custom attributes

Question

I have a model with attachments:

class Project < ApplicationRecord
  has_many_attached :images
end

When I attach and save the image I also want to save an additional custom attribute - display_order (integer) with the attached image. I want to use it to sort the attached images and display them in the order I specified in this custom attribute. I've reviewed ActiveStorage source code for #attach method as well as ActiveStorage::Blob model but it looks like there is no built in method to pass some custom metadata.

I wonder, what's the idiomatic way to solve this problem with ActiveStorage? In the past I would usually just add a display_order attribute to the ActiveRecord model which represents my attachment and then simply use it with .order(display_order: :asc) query.

Answer 1

If you need to store additional data with each image and perform queries based on that data, I’d recommend extracting an Image model that wraps an attached file:

# app/models/project.rb
class Project < ApplicationRecord
  has_many :images, dependent: :destroy
end

# app/models/image.rb
class Image < ApplicationRecord
  belongs_to :project

  has_one_attached :file
  delegate_missing_to :file

  scope :positioned, -> { order(position: :asc) }
end

<%# app/views/projects/show.html.erb %>
<% @project.images.positioned.each do |image| %>
  <%= image_tag image %>
<% end %>

Note that the example view above causes 2N+1 queries for a project with N images (one query for the project’s images, another for each image’s ActiveStorage::Attachment record, and one more for each attached ActiveStorage::Blob). I deliberately avoided optimizing the number of queries for clarity’s sake.